1. Field of the Invention
The present invention relates generally to wireless communications, and in particular to multiple antenna radar signal detection.
2. Discussion of the Related Art
Wireless local area network (WLAN) devices coexist with radar systems in the 5 GHz frequency bands. Radar systems could be used by military, aviation, meteorological, and other governmental agencies. Because of the importance of these radar systems, interference mitigation techniques are required to enable WLAN devices to share these frequency bands. In general, WLAN devices are required to detect an interference with a radar source and avoid using the frequencies used by that radar source.
To this end, various regulatory standards (e.g. the draft European Telecommunications Standards Institute (ETSI) EN 301 893, version V1.2.1, published 2002) require that a dynamic frequency selection (DFS) feature be incorporated in 5 GHz WLAN devices. This DFS feature should switch operating channels in the presence of co-channel radar and uniformly spread operation across a wide frequency range.
Various guidelines for radar detection have been proposed. For example, one proposed guideline includes detecting and avoiding only radar signals above a certain pre-defined threshold, such as −62 dBm. In one implementation, detection is based on a simple algorithm to determine whether there are any instances of signals above the −62 dBm threshold during a ten second startup listening period. Another proposed guideline includes periodically suspending all network traffic during normal operation and listening in a startup mode for any signals above the −62 dBm threshold level. Unfortunately, because of increased network traffic in the 5 GHz frequency band and the need for increased bandwidth among WLAN devices, these proposed guidelines are generally unsatisfactory.
Therefore, a need arises for improved radar detection and avoidance techniques.